WASHINGTON — President-elect Donald J. Trump’s choice of a fossil-fuel advocate and climate-change denier to head the Environmental Protection Agency comes at a moment when the American energy market has already shifted away from the most polluting fossil fuels, driven more by investors and economics than by federal regulations.

Those market forces could make Mr. Trump’s promise to create at least half a million energy jobs a year in the nation’s coal mines and oil shale fields all but impossible.

But if Mr. Trump’s promised jobs are unlikely to materialize, the impact on the planet from his policies would be significant. Without additional government policies, energy and environmental experts say, the shift from coal, oil and natural gas will not be rapid or substantial enough to stave off the worst impacts of a warming atmosphere, including rising sea levels, more powerful storms, more devastating droughts and food and water shortages.

“The good news is that on its own, the U.S. economy has become less carbon intensive, and that trend will continue overall,” said Robert N. Stavins, the director of the environmental economics program at Harvard University. The bad news, he said, is that markets alone will not lower emissions enough to offset the worst impacts of global warming.

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Scott Pruitt, President-elect Donald J. Trump’s choice to lead the Environmental Protection Agency, at Trump Tower in Manhattan on Wednesday.CreditStephen Crowley/The New York Times

President Obama’s Clean Power Plan was already criticized for not doing enough. Even if the plan was implemented, it would not reach the targets set under last year’s Paris climate change accord, which committed nearly every country to take action to curb global warming. The targets “will be unachievable,” Mr. Stavins said.

“Mr. Pruitt will be deeply involved in the implementation of President-elect Trump’s energy plan, which will move America toward energy independence, create millions of new jobs and protect clean air and water,” the statement said. “Mr. Pruitt will ensure that we conserve our natural habitats, reserves and resources, while unleashing an energy revolution that will bring vast new wealth to our country.”

That rebalancing of priorities, the president-elect said, will create “at least a half million jobs each year” and “$30 billion in higher wages.”

The irony of Mr. Pruitt’s zeal to target President Obama’s climate change and environmental rules, which focus on reducing carbon pollution from coal-fired power plants, is that many of the nation’s largest electric utilities — the entities that would be regulated under the plan — have already begun plans to shutter coal plants and build new wind and solar farms.

Even the chief executives of coal companies agree that Mr. Pruitt can only do so much to restore the industry.

Mr. Pruitt “is going to do what needs to be done at the E.P.A. — to cut the numbers of bureaucrats there who have done nothing but write regulations daily, and send them back to the radical environmentalists who wrote them,” said Robert E. Murray, the chief executive of the Ohio-based Murray Energy Corporation.

However, he added, “Coal can’t come back to where it was.”

The plummeting cost of wind and solar energy, helped along by federal tax incentives, has led to a boom in the use of such “no-carbon” power sources. And the nation’s largest electric utilities, many of which have joined Mr. Pruitt in his lawsuit against the climate regulations, have at the same time realigned their long-term investment strategies.

Nicholas Akins, chief executive officer of American Electric Power, an Ohio-based electric utility that generates power in 11 states, said in an interview shortly after Election Day that his company is making investments in energy generation aimed at 20, 30 and 40 years from now. Whether or not Mr. Trump dismantles the Clean Power Plan, he said he assumes that in the long run, carbon pollution will eventually be regulated.

“Clean Power Plan or not, there will be something in the future on carbon control. So there’s no question that the industry is moving forward with cleaner energy,” he said. “We will not be building large coal facilities. We’re not stopping what we’re doing based on the new administration. We need to make long-term capital decisions. I don’t think the course will change.”

But company-driven shifts alone will still not be enough to create the steep drop-off in carbon pollution that scientists say is necessary. The use of wind power grew by more than 100 percent between 2010 and the end of 2015, while the use of large-scale solar grew by more than 20 times in that same period, according to the Energy Information Administration. But renewable sources, excluding hydroelectric power, still only represent a small fraction of the American energy economy, providing just a little more than 7 percent of the country’s electricity.

Carbon dioxide emissions peaked in 2007 at six billion metric tons, declining slightly to 5.4 billion metric tons by 2014. But they would need to decline to about 4.8 billion metric tons annually by 2025 and 1.2 billion metric tons annually by 2050 if the United States is to meet its pledges under the Paris accord.

“To get there would require reducing emissions about 5 percent per year over the next decades. In order to reduce that fast, we would need to be avoiding new fossil fuel infrastructure and actively shutting down old fossil fuel infrastructure before the end of its natural life,” said Andrew Jones, the director of Climate Interactive, a research firm. “That’s not possible without aggressive federal policy.”

At the same time, analysts are skeptical that Mr. Trump’s efforts to roll back the climate change rules would bring back the tens of thousands of mining jobs that have been lost in the market shift away from coal, let alone create large numbers of new jobs. Electric utilities like American Electric Power turned away from investing in coal largely because of the glut of cheap natural gas, thanks to hydraulic fracturing, or fracking.

“The market defines the opportunities for coal,” said Kevin Book, an analyst with ClearView Energy Partners, a nonpartisan research firm. “Electric utilities that have shut down coal plants are not going to reopen them. Mines that have been mothballed because they are not economic are not going to be taken out of mothballs.”

He said coal could at least remain a part of America’s energy mix if Mr. Pruitt made headway in removing cumbersome regulations — and if he could successfully strip away subsidies for renewables. Last year, the federal government paid out $2.2 billion in tax incentives to the industry and $1 billion to the solar industry. The wind incentive is set to start declining in value next year until it ends in 2020, while the investment credit for solar is to phase out between 2019 and 2022.

But despite the opposition of the coal industry and incoming administration to climate change policy, the tax incentives, which have been enacted by Congress in both Democratic and Republican majorities for over a decade, are unlikely to disappear. Among their greatest beneficiaries are the windswept, sun-soaked districts in Republican strongholds like Kansas, Texas and Arizona, and Rust Belt districts that manufacture wind turbines and solar panels.

“I don’t see those renewable tax incentives going away anytime soon,” Mr. Book said. “Voters in many of these Trump districts are benefiting from them.”